This application is based on applications No. 11-44631 filed in Japan on Feb. 23, 1999 and No. 11-45790 filed in Japan on Feb. 24, 1999, the content of which incorporated hereinto by reference.
The present invention relates to a battery pack including a protective component such as a thermal fuse or a PTC.
A battery pack includes a protective component to prevent its use under abnormal conditions. The protective component cuts the electric current off if the temperature of the battery raises abnormally high or the current is abnormally high. A thermal fuse or a PTC is used as this type of protective component. A thermal fuse does blowout so the current is cut if the battery temperature goes higher than a predetermined temperature. A PTC raises its electrical resistance rapidly so the current hardly flows if the temperature raises due to a high current.
A battery pack with built-in plural cylindrical batteries, as shown in FIG. 1, includes a built-in protective component 103 at the space between batteries 124 in a case 125. The protective component 103 can be built-in using the cleavage space between the cylindrical batteries efficiently. However, for a battery pack with built-in rectangular batteries, as shown in FIG. 2, since there is no space between the batteries, a space is provided between a battery 224 and a case 225 such that a printed circuit board 226 is placed therein, and a protective component 203 for the batteries 224 is provided on the printed circuit board 226.
The battery pack with the structure as shown in FIG. 2 requires a larger case 225, since it needs an extra space for providing the built-in protective component 203. In addition, it is difficult to fix the printed circuit board 226 and the protective component 203 at predetermined position between the case 225 and the battery 224 without displacing them. If the printed circuit board 226 or the protective component 203 are moved inside of the case 225, it would deteriorate the reliability, because the vibrations might cause malfunction. Furthermore, as shown in FIG. 2, the battery pack in which the protective component 203 is between the side of the battery 224 and the case 225 requires that the protective component 203 be separated from a terminal 208 of a sealing plate 205. Consequently the connection of the protective component 203 to the terminal 208 of the sealing plate 205 is troublesome, and an elongated lead plate 227 is required.
The present invention has been developed to solve these drawbacks. The object of the present invention is to provide a battery pack with a built-in protective component, which is wholly compact and includes a protective component built-in.
Further, another important object of the present invention is to provide a battery pack with a built-in protective component, in which the protective component can be fixed at a predetermined position without being moved thereafter.
Furthermore, another important object of the present invention is to provide a battery pack with a built-in protective component, in which the protective component can be connected to terminals of a sealing plate via short lead wire.
Rechargeable batteries like lithium ion rechargeable batteries, nickel hydrogen batteries, or nickel cadmium batteries are provided with a safety valve to prevent the explosion of an outer sheathing case if used under abnormal conditions. The safety valve opens to exhaust the gas inside of the battery if the internal pressure of the battery is abnormally high. Sometimes the internal pressure of a battery reaches an abnormally high level when gas is produced inside of the battery by over-current flow or overcharge. If the internal pressure of the battery is high, it is necessary to exhaust the gas by opening the safety valve since the pressure would lead to a dangerous condition causing the destruction of the sheathing case.
When the safety valve opens, the gas inside of the battery will be exhausted. At that time, solution may also be exhausted together with the gas. The electrolyte exhausted from the battery can flow into a charger on which the battery is mounted and damage the charger or electronic device.
If the electrolyte touches contact points of terminals, it corrodes them and causes insufficient contact. Also, if the electrolyte adheres to the printed circuit board, it cause some drawbacks like corrosion of the conductive portion or short circuits at the conductive portion due to migration.
In order to prevent these drawbacks, some chargers have been developed such as a charger provided with a drainage to easily exhaust the leaked electrolyte. The drainage of the charger can prevent large amount of leaked electrolyte to collect inside of the case. However it cannot exhaust the electrolyte completely. The electrolyte leaked from the battery adheres to the terminal contact of the charger and inner surface of the case, thus causes a malfunction. Further, it is difficult for electronic devices with built-in batteries inside of the case to provide a drainage for draining the electrolyte easily. For these reasons, a malfunction of electronic devices due to electrolyte leaked from batteries and accumulated inside of the case may occur.
The present invention has been been developed to solve these drawbacks. The second object of the present invention is to provide batteries which absorb electrolyte leaked from batteries so as to effectively prevent the damage of the electronic device due to the electrolyte.
The above and further objects and features of the invention will more fully be apparent from the following detailed description and accompanying drawings.
The battery pack with a built-in protective component of the present invention comprises a cell, a terminal holder and a battery protective component. The cell tightly seals an opening of a sheathing case with a sealing plate which has a terminal protruding from its surface. The terminal holder is arranged so that it covers the sealing plate of the cell, providing storage space to include the protective component between the sealing plate and the terminal holder. The terminal holder is made of an insulating material. The protective component is set in the storage space provided between the terminal holder and the sealing plate, except for a terminal portion, in which the lower part of the protective component is positioned lower than the upper end of the terminal.
The battery pack with the built-in protective component of this structure has an overall compact size even with a built-in protective component. In addition, the protective component is mounted at a predetermined position so that it does not move around thereafter. These features are achieved by a battery pack having a storage space between the sealing plate and the terminal holder, and by the protective component being positioned, other than the terminal portion, so that its lower portion is lower than the upper end of the terminal. The cell with its terminal protruding from the sealing plate is provided with the terminal holder while it covers the sealing plate so that storage space is defined provided, except where the terminal is located, by virtue of a protruding terminal. The battery pack of the present invention uses this storage space to store its protective component. The battery pack of this structure has an overall compact size while including its protective component inside within a fairly reduced space, utilizing a unique structure of the cell and the terminal holder so that the space can be effectively used.
Furthermore, the above battery pack has another advantageous feature in that the protective component is located and maintained at a predetermined position in ideal conditions regardless of the outer shape of the batteries. A storage space s provided for the protective component by configuring the terminal holder and peripheral structure of the sealing plate of the cell. Moreover, the battery pack of the present invention is still advantageous for easy connection with the protective component using a short lead wire, because the protective component can be placed near the terminal of the sealing plate.
The battery pack employs, for example, a thermal fuse or a PTC, as the protective component, and provides the protective component preferably in a storage space at the lower portion of the terminal holder, so that the protective component is close to the sealing plate of the cell.
Furthermore, the battery pack of the present invention may provide a preservation space between the terminal holder and the sealing plate such that an absorbent material is placed there to further prevent the damages caused by electrolyte.
The battery pack with this structure has the advantageous ability to absorb the electrolyte leaked from the battery and thus to effectively prevent the damages to the electronic device due to the electrolyte. In addition, the battery pack of this structure also has the advantageous ability to efficiently prevent damage to the electronic device due to the electrolyte by effectively absorbing the electrolyte of the battery, because an absorbent material is placed in the preservation space provided between the sealing plate of the cell and the terminal holder.
Nevertheless, because the preservation space for absorbent material is provided by the unique configuration of the terminal holder and the peripheral structure of the sealing plate of the cell, the battery pack can use this space so efficiently that the absorbent material is provided, and can easily and precisely locate the absorbent material at prescribed location.